Reduction of waste solutions has been strongly desired in recent years in the medical or printing industrial field from the viewpoint of environmental protection and space saving. Accordingly, techniques concerning a photothermographic material for medical diagnosis and photography which can be exposed efficiently with a laser/image setter or a laser/imager and can form a clear black image exhibiting high resolving power and sharpness have been desired. Such a photothermographic material can offer to customers a simpler and environmentally benign heat development processing system in which the use of solution-based processing chemicals can be done away with.
On the other hand, techniques of a semiconductor laser which have rapidly progressed in recent years have made it possible to realize a compact size image output apparatus. Techniques of infrared ray-sensitive photothermographic silver halide photographic materials in which a semiconductor laser can be used as a light source have of course been developed. For example, techniques of spectral sensitization are disclosed in JP-B-3-10391 (the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-B-6-52387, JP-A-5-341432 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-6-194781, JP-A-6-301141 and EP-A-803764. Techniques for preventing halation are disclosed in JP-A-7-13295 and U.S. Pat. No. 5,380,635. Photosensitive materials which are premised on infrared ray exposure can largely reduce the absorption of sensitizing dyes and antihalation dyes in a visible ray region and substantially colorless photothermographic or thermographic materials can be manufactured easily.
However, there is a problem even in these photothermographic materials such that storage stability before and after image formation is not satisfactory, therefore, the improvement of such a problem has been desired.